if(isset($_POST['send-serial']))
{
   add_filter( 'wp_mail_content_type', 'wpdocs_set_html_mail_content_type' );

   $user_id = get_current_user_id();
   $user = get_userdata( $user_id );

   $firstname = get_user_meta( $user_id, 'first_name', true );
   $lastname = get_user_meta( $user_id, 'last_name' , true );
   $tel = get_user_meta( $user_id, 'billing_phone' , true );
   $useremail = $user->user_email;

   $serailProduct = $_POST['serail-product'];

   $headers = array(
    'From: xxxxx.xx@xxx.com',
    'CC: xxxxx@gmail.com',
    'CC: xxxxx@gmail.com'
   );

   $to = array(
    'xxxxx.xxxx@gmail.com'
    );
   $subject = 'Serial Number';
   $body = '<p>Serial Number product ' . $serailProduct . '</p>
   <p>Name : ' . $firstname . ' ' . $lastname . '</p>
   <p>Email : ' . $useremail . '</p>
   <p>Tel : ' . $tel . '</p>';

   wc_add_notice('<strong>Success:</strong> Your Serial Product has sended ', 'inkfool');
   wp_mail( $to, $subject, $body, $headers );

   // Reset content-type to avoid conflicts -- https://core.trac.wordpress.org/ticket/23578
   remove_filter( 'wp_mail_content_type', 'wpdocs_set_html_mail_content_type' );

   function wpdocs_set_html_mail_content_type() {
       return 'text/html';
   }
}